Single-walled carbon nanotubes (SWCNTs) have, over the past several years, generated considerable interest as a result of their mechanical and electronic properties. SWCNTs can be one of two electronic types, either metallic or semiconducting, depending on their chirality. Significant progress has been made at controlling SWCNT structure during nanotube growth, but post-synthetic processing steps are still required to extract carbon nanotubes of particular electronic types at high purity levels. In order to achieve the wide-spread industrial use envisioned for SWCNTs, semiconducting and metallic species must be isolated efficiently and at extremely high purities. While methods exist to separate both semiconducting and metallic SWCNTs, much of the interest in carbon nanotubes lies in their semiconducting applications. For instance, incorporation of semiconducting single-walled carbon nanotubes has shown to improve the functionality of a diverse array of technologies ranging from transistors to molecular detectors. Numerous separation techniques have been developed, including electrophoresis, gel chromatography and DNA wrapping. One particular prior separation method, density gradient ultracentrifugation (DGU), involves several time-consuming and labor-intensive steps, including the creation of a linear density gradient. Furthermore, the extraction of high purity semiconducting species requires complex fractionation procedures and associated equipment costs.
Improving the fidelity and yield of DGU separations has proven to be an often laborious process. Accordingly, there remains an on-going effort in the art to develop a nanotube separation system to better utilize the benefits available through DGU.